Thermoplastic adhesives, otherwise known as “hot melt” adhesives, have been widely used in industry for various applications. Hot melt adhesives may be dispensed in many ways, but often are dispensed by systems having one or more dispensing guns coupled by heated hoses to a melter. The melter may include a tank for melting and storing the hot melt adhesive, a manifold having multiple distribution outlets for coupling with a heated hose, and a pump for transferring the hot melt adhesive from the tank through the manifold. Adhesive material may be supplied to the melter in solid or semi-solid form, where it is heated and melted to a desired temperature. Examples of such melters are the ProBlue™ melter units available from Nordson Corporation of Westlake, Ohio.
In use, conventional melters may be fed adhesive material in the form of pellets through an air or vacuum supply conduit. The pressurized airflow used to force pellets through the supply conduit is then removed from the melter via an exhaust passage. In conventional melters, the exhaust passage is located in the path of the pellets. This type of configuration limits the flow area for the exhaust passage and may cause excessive turbulent airflow to develop within the melter.
The turbulent air flow and the stickiness of adhesive pellets in the heated environment of conventional melters cause the dust and fines of the adhesive to accumulate on the surfaces of the supply conduit and the exhaust passage. This accumulation of dust and fines, in turn, may lead to rapid clogging of the exhaust opening and/or a filter associated with the exhaust opening, thereby requiring frequent cleaning of passages and replacement of the filter. This may result in downtime to facilitate cleaning of the adhesive dispensing system.
The problem with clogging of filters may be especially noticeable in melters that have a relatively small size, and where the top wall or the lid offer a relative small surface area. Melters of this type may, for example, have a configuration in which the supply conduit and exhaust passage are concentric with one another and in which the exhaust passage surrounds the supply conduit. In melters of this type, the dust and fines of the adhesive may impact the inner surfaces of the supply passage and accumulate on those surfaces, which may require frequent cleaning, as a result. In addition, in melters of this type, the dust and fines may accumulate on a filter associated with the supply conduit, thereby requiring frequent replacement of the filter.
It is desirable, therefore, to have an adhesive dispensing system that addresses these and other problems associated with conventional melters of the type described above.